Sputter deposition is commonly used for forming thin-layer films or well-defined thickness and crystal orientation on a substrate. For example, thin-film magnetic recording media or discs are manufactured by sputtering a series of layers, such as an underlayer, a magnetic recording layer and a protective overlayer, on a substrate disc.
In a sputtering operation, a gas--typically argon--is introduced into the sputtering chamber to serve as a medium in which gas discharge is initiated and sustained. By placing a negative bias on the target, positive ions in the discharge are drawn to the cathodic plate, where they eject neutral atoms through momentum transfer. These atoms pass through the discharge region to be deposited on a substrate. Additional particles, including negative ions, are also discharged from the target, and may be accelerated toward the substrate, to bombard the film being deposited. The sputtering plasma can be focused, to achieve greater plasma density and stability, by applying a magnetic field across the target. This approach, known as magnetron sputtering, is useful in achieving high sputtering rates.
In a typical sputtering assembly, the substrate is placed near the target, with the target surface confronting the substrate surface. The region between the target and substrate is shielded, e.g., by an annular ring extending between the two, to capture wide-angle deposition material that is not directed against the target and which would otherwise be ejected into the sputtering chamber. Shields of this type typically have smooth inner surfaces on which the wide-angle material is deposited.
Because of relatively rapid accumulation of material on the shield's inner surface, shields of this type must be removed from the sputtering apparatus and cleaned frequently, e.g., by sand-blasting. A more serious problem can arise in the case of deposited carbonaceous material, such as the carbon deposits that form when a carbon overcoat is sputtered onto a magnetic thin-film medium. The carbon deposits can easily flake off during a sputtering operation. When flaked-off deposits fall into the sputtering plasma, the deposits can explode, meteor-like, throwing off particles in all directions that can result in damage to the deposition surface. This can be observed as plasma arcing during the sputtering operation.
It would therefore be desirable to provide a sputtering shield, particularly for use in carbon deposition, that effectively prevents such arcing, and increases the amount of material that can safely accumulate on the shield surface during a sputtering operation.